* inputs, with counts equal to the result of applying {@code countFunction} to the inputs.
   * Elements are added in encounter order.
   *
   * <p>If the mapped elements contain duplicates (according to {@link Object#equals}), the element
   * will be added more than once, with the count summed over all appearances of the element.
   *

   * {@code initialCapacity} values without resizing. The returned builder is not thread-safe.
   *
   * <p><b>Performance note:</b> When feasible, {@code initialCapacity} should be the exact number
   * of values that will be added, if that knowledge is readily available. It is better to guess a
   * value slightly too high than slightly too low. If the value is not exact, the {@link

   * computation is already complete, immediately.
   *
   * <p>The callback is run on {@code executor}. There is no guaranteed ordering of execution of
   * callbacks, but any callback added through this method is guaranteed to be called once the
   * computation is complete.
   *
   * <p>Example:
   *
   * <pre>{@code
   * future.addCallback(
   *     new FutureCallback<QueryResult>() {

   * {@code initialCapacity} values without resizing. The returned builder is not thread-safe.
   *
   * <p><b>Performance note:</b> When feasible, {@code initialCapacity} should be the exact number
   * of values that will be added, if that knowledge is readily available. It is better to guess a
   * value slightly too high than slightly too low. If the value is not exact, the {@link

   * will remember the first duplicate key we encountered. All later calls to buildOrThrow() can
   * mention that key with its values. Further duplicates might be added in the meantime but since
   * builders only ever accumulate entries it will always be valid to throw from buildOrThrow() with
   * the first duplicate.
   */

    List<String> alreadyThere = Lists.newArrayList("already", "there");
    List<String> freshlyAdded = Lists.newArrayList("freshly", "added");

    boolean changed = Iterators.addAll(alreadyThere, freshlyAdded.iterator());

    assertThat(alreadyThere).containsExactly("already", "there", "freshly", "added");
    assertTrue(changed);
  }

  public void testAddAllToSet() {

    }

    /**
     * The number of permutations with repeated elements is calculated as follows:
     *
     * <ul>
     *   <li>For an empty list, it is 1 (base case).
     *   <li>When r numbers are added to a list of n-r elements, the number of permutations is
     *       increased by a factor of (n choose r).
     * </ul>
     */
    private static <E> int calculateSize(

  }

  /** Runs a runnable without any permissions. */
  public void runWithoutPermissions(Runnable r) {
    runWithPermissions(r);
  }

  /** A security policy where new permissions can be dynamically added or all cleared. */
  public static class AdjustablePolicy extends java.security.Policy {
    Permissions perms = new Permissions();

    AdjustablePolicy(Permission... permissions) {

 * that every {@code Runnable} that is {@linkplain #add added} will be executed after {@link
 * #execute()} is called. Any {@code Runnable} added after the call to {@code execute} is still
 * guaranteed to execute. There is no guarantee, however, that listeners will be executed in the
 * order that they are added.
 *
 * <p>Exceptions thrown by a listener will be propagated up to the executor. Any exception thrown

 * equivalent elements are added to it, it is undefined which will come first in the output.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
final class TopKSelector<
    T extends @Nullable Object> {

  /**
   * Returns a {@code TopKSelector} that collects the lowest {@code k} elements added to it,